The new Splunk REST modular input (which is still beta) is very nice and usefull. I'm using it to poll jmx via Jolokia webapp, and it works great.
But, there are some cases you want to poll the REST interface by using POST request. for example, if I want to query multiple MBeans. Jolokia supports this only via POST request. I'm sure that there are many more examples.
"Jolokia supports this only via POST request"....that is not really RESTful then. POST should be used for creating. Actually , just browsing the Jolokia docs , the Jolokia interface is mentioned as only being "REST Like".
I might add a non RESTful option to support POSTs and Body Content. It's a trivial addition.